$ A = \left[\begin{array}{rrr}-2 & -1 & 4 \\ -2 & 0 & 0 \\ 1 & -1 & 3 \\ 2 & 4 & 2\end{array}\right]$ What are the dimensions of matrix $ A$ ?
Solution: The first dimension is the number of rows in the matrix. How many rows does $ A$ have? The second dimension is the number of columns in the matrix. How many columns does $ A$ have? So, $ A$ is a 4 $\times$ 3 matrix.